The present invention relates to a low-cost azimuth signal generator suitable for use in an automobile navigation system or the like.
Conventional azimuth signal generators are, in general, geomagnetic azimuth sensors (such as a magnetic compass, a flux valve, etc.) and a gyrosyn compass. The gyrosyn compass is employed primarily for aircrafts and has an arrangement in which an azimuth gyro is controlled using a signal detected by a flux valve (a sensor mounted on an airplane at a position where the influence of electricity and magnetism is slight, such as the wing tip or tail, for detecting the direction of the horizontal component of the vector of geomagnetism) so that the spin axis of the azimuth gyro is always directed to the direction of the horizontal component of geomagnetism to eliminate a drift of the azimuth gyro in the direction of its spin axis (which is attributable to friction of gyro bearings, imbalance of the gyro structure, the influence of rotation of the earth, and so forth), thereby accurately detecting the angle of heading of the plane. No detailed description will be given of the conventional azimuth signal generators, because they are well-known in the art.
The conventional geomagnetic azimuth sensors are low-cost but they are susceptible to the influence of magnetic fields other than geomagnetism, such as magnetic fields which are developed by electrical machinery and apparatus of vehicles and electric railways, and consequently, measurement errors remain large unless measured values are properly processed. On the other hand, the gyrosyn compass is free from the influence of such magnetic fields except earth magnetism but is expensive, in general, and hence is not suitable for use in a car navigation system, because the azimuth gyro has a high precision, complex structure for high-speed rotation and therefore is costly.